One process for applying to a textile or fabric, liquor such as water-repellent chemicals or dyes that have a low or no affinity for the fibres in the fabric, is known as the padding process. The padding process is an immersion process that consists essentially of two steps. The first step, known as the “dip”, is when the fabric is immersed in the required liquid in a padding tank to achieve thorough impregnation of the fabric. The fabric is passed under a submerged roller in the padding tank full of the required liquid, which may be a dye or water-repellent agent.
The second step, known as the “nip”, consists of passing the fabric out of the padding tank and then between two rollers, known as pad mangles, to squeeze out air and force liquid into the fibres of the fabric or material. As the fabric passes through the pad mangles, at speeds of up to 50 m per minute, the excess liquid squeezed out is sent back along the fabric. For the process to be effective and even, sufficient liquor needs to be adsorbed on to the fabric before excess is squeezed out by a mangle.
Previous processes for applying a water repellent agent to a fabric in a pad bath have suffered from the problem that the surfactant on and in the fabric inhibited the attainment of good water-repellent properties. One earlier approach to reducing such inhibition was to use a wetting agent that was sensitive to heat and thus rendered non-wetting. This occurs either by evaporation or irreversible decomposition in the heat treatment process applied to the fabric after padding. The products that have been used in the past are the commercially available amine oxide surfactants, such as Cetapol OX20 (Avocet Dyes Ltd), Sulfanole 270 (Omnova Solutions Inc), or volatile surfactants such as Surfynol 61 (Air Products). However, these wetting agents are limited in their ability to provide a strong wetting at low usage levels. Increasing the amounts of wetting agent used merely leads to long periods of heat treatment being needed.